A controller for controlling the operation of a hard disk drive is capable of generating a random number using the hard disk drive. Initially the hard disk drive is disabled from performing a read-ahead operation. Random addresses on the hard disk drive are generated from the output of the pseudo-random number generator. Read-verify commands is sent to the hard disk drive to perform a read-verify operation of reading and verifying the data stored in the sectors of the hard disk drive at the random addresses without returning the data. The disk access times taken by the hard disk drive to access the sectors are measured. A deskewing process is performed on a plural number of disk access time measurements to generate a random number.